1. Field of the Invention
The present invention relates to a plasma etching system and method for applying a plasma etching treatment to a substrate such as a semiconductor wafer, particularly to an improvement in a shower electrode of a high flow rate type used as an upper electrode of a parallel plate electrode type etching apparatus.
2. Description of the Related Art
A parallel plate electrode type plasma etching apparatus comprising a pair of electrodes facing each other is known to the art as an etching apparatus for a semiconductor wafer. In the etching apparatus of this type, a wafer is disposed on a lower electrode, and a plasma-forming gas such as a halogen gas or a freon gas is spurted toward the wafer through a large number of spurting holes formed in an upper electrode acting as a shower electrode. Also, a high frequency voltage is applied between the upper and lower electrodes so as to convert the gas into a plasma used for etching the wafer.
In the conventional etching apparatus, however, the upper electrode, i.e., shower electrode, is designed to achieve mainly a uniform plasma generation. In other words, sufficient attentions are not paid to the gas flow rate, the pitch of the gas spurting holes and the diameter of the gas spurting hole adapted for an optimum wafer etching.
In recent years, the pattern of a semiconductor device tends to become finer and finer. An anisotropic etching having a high aspect ratio is utilized for the manufacture of a semiconductor device having a finer pattern. For achieving an anisotropic etching with a high aspect ratio, it is necessary to set the inner pressure of the process chamber at a low level, leading to a plasma polymerization of the treating gas. As a result, a polymer containing C, O and F is deposited on the circumferential wall of the spurting holes. The deposited polymer film gradually grows with increase in the plasma discharge time to form a polymer film having a thickness of scores of microns. Finally, the polymer film drops in the form of lumps from the upper electrode onto the wafer so as to contaminate the wafer and, thus, to lower the yield of the semiconductor device.
What should also be noted that the shower electrode used in the ordinary etching cannot be used for the anisotropic etching with a high aspect ratio, making it necessary to prepare a shower electrode used exclusively for the anisotropic etching.